The subject matter disclosed herein relates to a system for improving the cooling performance of a turbine engine by utilizing an ejector system that increases compressor air entrainment efficiency. The axial location, or stage, at which compressed air is diverted from a compressor for cooling a multi-stage turbine in a turbine engine is determined by the pressure required to drive the specific systems to be serviced by that air. Diverting compressed air from the earliest possible stage of a compressor will increase overall turbine efficiency by reducing the amount of compressor work invested in the diverted air, as well as reducing the temperature of the diverted and, thus, the delivered compressed air. Therefore, it is desirable to achieve the system supply pressure from the earliest and lowest pressure stage of the compressor.
Known systems divert compressed air from plural ports in a multi-stage compressor to provide cooling and/or sealing air to an associated multi-stage turbine. These systems utilize a low pressure extraction flow path for conducting compressed air from a lower pressure, lower temperature stage of the compressor to the turbine and a high pressure extraction flow path for conducting compressed air from a higher pressure, higher temperature stage of the compressor to the turbine. A crossover flow path may be used to interconnect the low pressure extraction flow path, and the high pressure extraction flow path. Such a crossover allows selective control of the compressed air delivered to the multi-stage turbine such that a desired pressure and an economic mixture of air are diverted from the compressor.
The low and high pressure air is combined through the use of an ejector system which utilizes the momentum of motive flow of the high pressure air through a nozzle to create a suction flow of low pressure air surrounding the nozzle. Interlayer shear operates between the high and low pressure air flow streams within the ejector system resulting in entrainment (suction flow) of the low pressure air with the high pressure flow stream. It is therefore desirable to increase the entrainment of low pressure air flow within the high pressure air flow, to improve the efficiency of the ejector system.